how much coins I need for stacking?
IIRC it's 100,000. Could be wrong. Maybe someone else could confirm?
Whitepaper says 2.000.000 (2mil).
As someone mentioned earlier, I think 2mil is (or will be) the new masternode requirement. I know staking requires much less. Fairly sure it was mentioned a while ago in the Linda Slack channel that's it's 100,000 but I've never tried staking less than that so I can't confirm.